The present invention, in some embodiments thereof, relates to methods of generating oligodendrocytes or oligodendrocytes progenitors from mesenchymal stem cells and cell populations comprising same.
Oligodendrocytes are important cells in the CNS that synthesize multilamellar myelin membranes that ensheath axons and therefore play an important role in the development and function of the CNS. Demyelination disrupts nerve conduction and leads to nerve degeneration which is associated with various disorders including Multiple Sclerosis (MS).
Oligodendrocytes are derived from multipotent neural progenitor cells. Various transcription factors and signaling pathways have been associated with this process, including Olig1, NKX2.2, SHH, Wnt and Notch (2).
For example, early oligodendrogenesis is regulated by the basic helix-loop-helix transcription factors Olig1 and Olig2. The expression of these transcription factors persists as oligodendrocyte progenitors leave the ventricular zone and become mature oligodendrocytes. During the time when oligodendrocytes migrate into the white matter, they acquire the expression of two additional transcription factors, Sox10 and Nkx2.2. The expression of these two transcription factors directly regulates the expression of the myelin gene and the differentiation of oligodendrocytes.
Multiple Sclerosis is a disease caused by chronic autoimmune inflammatory process resulting in patches of demyelination that affects the central nervous system (11). Remyelination, a regenerative process in which axons in the CNS are reinvested with new myelin sheaths and pre-lesion architecture and functions are restored, is mainly mediated by a population of cell specific adult stem/progenitor cells that are called oligodendrocyte precursor/progenitor cells (OPC) or glial precursor/progenitor cells. These cells are distributed in the white and grey matter throughout adulthood. Failure of remyelination predisposes axons to degeneration, a reversible process which is associated with the progressive deterioration of the disease. Therefore, remyelination is considered an important clinical objective in MS in order to slow or prevent axonal degradation and to preserve long-term axonal survival in the brain and spinal cord.
Mesenchymal stem cells (MSCs) are a heterogeneous population of stromal cells isolated from multiple species, residing in most connective tissues including bone marrow, adipose, umbilical cord, placenta, amniotic fluid and perivascular tissues. MSC can differentiate into cells of the mesenchymal lineage, such as bone, cartilage and fat but, under certain circumstances, have been reported to acquire the phenotype of cells of the endodermal and neuroectodermal lineage, suggesting some potential for “transdifferentiation”. Within the bone marrow these cells are tightly intermingled with and support hematopoiesis and the survival of hematopoietic stem cells in acquiescent state (7). In addition, MSCs derived from the bone marrow, adipose tissue or the cord/placenta have unique properties after expansion in culture including their ability to modulate innate and adaptive immunity (8). Furthermore, MSCs migrate to sites of inflammation and protect damaged tissues, including the CNS, properties that supported their use as new immunosuppressive or rather immunoregulatory or anti-inflammatory agents for the treatment of inflammatory and immune-mediated diseases including autoimmune disorders (9).
Recent reports have demonstrated that MSCs also have the potential to differentiate into functional neuronal cells. MSCs have been shown to exert therapeutic effects in a variety of neurological diseases and dysfunctions in experimental animal models and more recently in pilot clinical trials. Their effects have been mainly attributed to immunosuppressive and neuroprotective functions. However, some studies demonstrated that neural differentiation of these cells increased their therapeutic effect in various instances. Therefore, the use of MSC-derived neuronal cells has a great potential as an easily accessible source of autologous cells for treatment of inflammatory and neurodegenerative disorders including Multiple Sclerosis, ALS and Parkinson's disease aiming for both cell mediated control of disease activity as well as regeneration of damaged or lost functions.
In experimental autoimmune encephalitis (EAE), an animal model of MS, treatment of mice with bone marrow derived MSCs resulted in significant suppression of disease manifestations in parallel with down-regulation of cell-mediated anti-self reactivity (9). The migration of bone marrow derived MSCs paralleled improvement of the clinical outcome of treated recipients (9). Using genetically transduced green fluorescent donors in these animal models, donor derived cells migrating into the brain acquired phenotypic markers of neurons, astrocytes and oligodendrocytes in parallel with improvement of clinical signs of disease as was also confirmed by histopathological evaluation of treated as compared with untreated controls. Interestingly, transplantation of glial committed progenitor into a viral model of MS resulted in some degree of remyelination (12), suggesting that the strategy of transplantation of oligodendrocytic progenitors is worthwhile pursuing.
Studies using injection of enriched and unmodified autologous bone marrow derived and more recently also adipose tissue derived MSC which can be prepared from liposuction intrathecally and intravenously suggests that some patients with otherwise resistant MS may benefit from treatment with autologous MSCs; however, complete restoration of all neurological deficits in patients with advanced and long-lasting disease has not yet been achieved (13). Iron nanoparticle (Feridex™) labeled MSCs injected intrathecally and intravenously could be documented in the brain by MRI, thus confirming that these cells can actively migrate into the central nervous system.
Liu et al [Dev Biol. 302:683-693, 2007] have reported oligodendrocytic differentiation of bone marrow derived mesenchymal cells. This study employed fetal cells and used transfection with the transcription factors Olig2 and NKX.2.
U.S. Patent Application No. 20100021434 teaches oligodendrocytic differentiation of bone marrow derived mesenchymal cells by incubation in N2 supplement and fibroblast growth factor (FGF).
International Patent Application WO2010111522 teaches mesenchymal stem cells which secrete and deliver microRNAs for the treatment of diseases.
International Patent Application WO2010144698 teaches expression of miRNAs in mesenchymal stem cells to induce neuronal differentiation thereof.